Masahiko Iizuka

Plasma concentrations of α-human atrial natriuretic polypeptide and cyclic GMP in patients with heart disease☆

Plasma concentrations of immunoreactive α-human atrial natriuretic polypeptide (iα-hANP) and cyclic guanosine monophosphate (cGMP) were measured in 70 patients with heart disease. Plasma concentrations of iα-hANP were directly related to the severity of heart disease (F = 29.61, p < 0.001). Plasma concentrations of iα-hANP were well correlated with pulmonary capillary wedge pressure (PCWP; r = 0.64, p < 0.001), mean pulmonary arterial pressure (PAP; r = 0.62, p < 0.001), and mean right atrial pressure (RAP; r = 0.75, p < 0.001). Plasma concentrations of cGMP were also directly related to the severity of heart disease (F = 13.61, p < 0.001) and highly correlated with plasma concentrations of iα-hANP (r = 0.73, p < 0.001). Plasma concentrations of cGMP were also closely correlated with PCWP (r = 0.69, p < 0.001), mean PAP (r = 0.61, p < 0.001), and mean RAP (r = 0.60, p < 0.001). The iα-hANP concentrations of plasma samples obtained from the coronary sinus were approximately fourfold higher than those of samples obtained from the pulmonary artery, whereas cGMP concentrations were comparable in plasma samples obtained from either site. Elevation of cGMP concentrations following intravenous infusion of synthetic α-hANP was comparable in plasma samples obtained from the coronary sinus and the pulmonary artery. These findings suggest that elevated plasma concentrations of iα-hANP in cardiac patients result from an increase in the secretion of ANPs, which is probably accelerated by elevation of right or left atrial pressure, and that plasma concentrations of cGMP reflect circulating levels of α-hANP.

ADP inhibits the sliding velocity of fluorescent actin filaments on cardiac and skeletal myosins.

We studied the effect of MgADP on the mechanical interaction of actomyosin in cardiac and skeletal muscles using an in vitro motility assay. The sliding velocities of fluorescently labeled actin filaments on rat cardiac and skeletal myosins were measured at various MgATP and MgADP concentrations. The filament velocity depended on MgATP concentration according to classic Michaelis-Menten kinetics with apparent Michaelis constants (Km) of 43 and 137 mumol/L and maximum velocity of 5.6 and 8.6 microns/s for cardiac and skeletal myosins, respectively. The presence of 2 mmol/L MgADP decreased the filament velocity and shifted the substrate concentration dependence of the velocity toward higher MgATP concentrations, yielding the inhibition constants of 194 and 478 mumol/L for cardiac and skeletal myosins, respectively. The activation energies determined by the temperature dependence of the velocity were 61 and 83 kJ/mol for rat V1 and rabbit cardiac myosins, which were similar to those of the dissociation rate constant of actomyosin-ADP complex reported in a solution study. The inhibition of the velocity by MgADP can be explained by the crossbridge scheme in which MgADP competes with MgATP for the substrate site on myosin molecules. In cardiac myosin, addition of a concentration of MgADP as low as 25 mumol/L significantly inhibited the velocity in the presence of 2 mmol/L MgATP, suggesting that increased intracellular MgADP may reduce the rate of crossbridge detachment, resulting in a decreased ATP consumption and an increased economy of force production under ischemic conditions. The present results support the idea that MgADP may be a physiologically important modulator of contraction in cardiac muscle.

Doppler echocardiographic-determined changes in left ventricular diastolic filling flow velocity during the lower body positive and negative pressure method

Changes in parameters of left ventricular (LV) diastolic filling flow obtained with Doppler echocardiography during the lower body positive and negative pressure method were analyzed in 15 patients (12 with coronary artery disease and 3 with dilated cardiomyopathy). Lower body pressure was altered at 5 steps (+20, +10, 0, -20 and -40 mm Hg vs atmospheric pressure). Pulmonary capillary wedge pressure measured with a balloon-tipped catheter was changed proportionally with lower body pressure during the procedures (p less than 0.01). Mean systemic arterial pressure was changed slightly during lower body positive pressure and negative pressure of -40 mm Hg. Heart rate was almost unchanged except at lower body pressure of -40 mm Hg. The peak velocity of LV early diastolic filling flow was changed with pulmonary capillary wedge pressure in an almost parallel fashion during the procedures (p less than 0.01). The peak velocity of LV late diastolic filling flow showed smaller changes than that of early diastolic filling flow. Changes in pulmonary capillary wedge pressure correlated positively with changes in the peak velocity of LV early diastolic filling flow (r = 0.759, p less than 0.01), but not with changes in the peak velocity of LV late diastolic filling flow (r = 0.039, not significant) during lower body negative pressure of -20 mm Hg. These data suggest that left atrial pressure is one of the important determinants of LV early diastolic filling flow in this acute clinical setting and that LV late diastolic filling flow is less sensitive to changes in left atrial pressure than LV early diastolic filling flow.

Collagen-stimulated human platelet aggregation is mediated by endogenous calcium-activated neutral protease.

To clarify the physiological role of calcium-activated neutral protease (CANP) in human platelets, we loaded the platelets with a Ca2+ -sensitive fluorescent dye, fura-2, and measured the degree of aggregation, cytosolic calcium ion concentration [( Ca2+]i), and proteolysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). At physiological concentration of Ca2+ (1 mM) in the incubation medium, [Ca2+]i was below 0.5 microM and platelet aggregation was not shown. Ionomycin (0.15 microM) or collagen (50 micrograms/ml), but not ADP (10 microM), sharply enhanced the [Ca2+]i to near 1 microM and caused the aggregation. A calcium entry blocker, verapamil, completely abolished both the [Ca2+]i rise and the aggregation. NCO-700, a membrane permeable inhibitor against cysteine proteases (including CANP), dose-dependently blocked the aggregation but did not change the [Ca2+]i transient. SDS-PAGE revealed that filamin, talin, and 70 kDa protein were specifically degraded when platelets were aggregated by ionomycin or collagen and that the proteolysis was not observed when the aggregation was blocked by verapamil or NCO-700. These data provided evidence that Ca2+ entry exceeding 0.5 microM is essential, but not sufficient per se, and that activation of cysteine protease, most likely CANP, is involved in the platelet aggregation by collagen or calcium ionophore.

Acute effect of percutaneous transluminal mitral commissurotomy on QT interval: Possible role of afterload in contraction-excitation feedback

Percutaneous balloon valvuloplasty for pulmonary or aortic stenosis results in QT prolongation, a finding supporting the presence of contraction-excitation feedback in man. Though afterload reduction alters the QT interval, the effect of changes in preload on ventricular repolarization is yet unknown. To test whether diastolic stretch modified ventricular repolarization, the change in the QT interval was determined in 15 patients who underwent percutaneous transluminal mitral commissurotomy (PTMC) for mitral stenosis. After successful PTMC, the QT interval was prolonged in five, shortened in two, and was unchanged in eight patients, but the mean QT interval in 15 patients did not change (406 +/- 31 msec versus 412 +/- 40 msec, p = NS). However, linear regression analysis revealed a strong correlation between changes in the QT interval and those in systemic vascular resistance (r = -0.83, p less than 0.01). These data indicated that changes in the QT interval after PTMC were small compared with those seen with valvuloplasty for pulmonary or aortic stenosis, and were dependent on afterload but not on preload.

Turnover of NAD in bacteria

Abstract The turnover of NAD was investigated in 4 bacteria; strains with different requirements for niacin and niacinamide: the niacinamide type, Staphylococcus aureus 209P, which prefers niacinamide to niacin, and Lactobacillus fructosus 353, which strictly requires niacinamide; the niacin type, Leuconostoc mesenteroides IFO 3426, which strictly requires niacin, and Escherichia coli B, which does not require niacin or niacinamide but synthesizes NAD via niacin. 1. 1. NAD turnover was found to occur in S. aureus and L. fructosus , as revealed by labeling and ‘chase’ experiments with [ 14 C]niacin and [ 14 C]niacinamide. 2. 2. In E. coli and L. mesenteroides no turnover of NAD was observed. 3. 3. NADP did not show any evidence of turnover in the four strains tested. 4. 4. The degradation product of [ 14 C]NAD in culture media of S. aureus and L. fructosus was examined and found to be exclusively [ 14 C]niacinamide.

Effects of new intravascular contrast agents on [Ca2+]i transients and contraction in cultured ventricular myocytes.

SummaryWe examined the effects of four kinds of intravascular contrast agents (amidtrizoic acid, iohexol, iopamidol, and ioxaglic acid) on [Ca2+]i transients (indo-1 fluorescence) and cell contraction (video motion analyzer), using cultured chick embryo ventricular myocytes. Exposure of ventricular myocytes to amidtrizoic acid (a conventional contrast agent) reduced the [Ca2+]i transients and the sensitivity of the contractile elements to [Ca2+]i. Ioxaglic acid (a low osmotic contrast agent) also reduced the [Ca2+]i transients, but did not significantly change the sensitivity of the contractile elements to [Ca2+]i. Neither iohexol nor iopamidol (nonionic contrast agents) reduced the [Ca2+]i transients, but both significantly decreased the sensitivity of the contractile elements to [Ca2+]i. A marked negative inotropic effect of amidtrizoic acid was caused by both calcium binding and hypertonicity. The less marked depression of contractility produced by ioxaglic acid is possibly the result of calcium binding, but is not caused by hypertonicity. The negative inotropism produced by nonionic contrast agents (iohexol and iopamidol) was due to hypertonicity, but not due to alterations in the [Ca2+]i transients.Exposure of ventricular myocytes to nonionic contrast agents (iohexol and iopamidol) slowed decay in the [Ca2+]i transients with increased end-diastolic [Ca2+]i. After washing out the nonionic contrast agents, these parameters returned to control levels. On the other hand, exposure to amidtrizoic acid decreased end-diastolic [Ca2+]i without changing decay time in the [Ca2+]i transients. After washing out amidtrizoic acid, there was a prolongation of half decay time in [Ca2+]i transients with a significant increase in end-diastolic [Ca2+]i and cell position. Diastolic dysfunction just after washout of amidtrizoic acid was possibly caused by an increase in [Na+]i due to sodium influx during exposure to the contrast agent.